Transports Québec officials say they suspect recent temperature fluctuations are to blame after concrete fell onto a car on Highway 40 from the Henri-Bourassa overpass yesterday.

"What we suspect ... is that it's the extreme weather conditions that we had the past two weeks ... caused the concrete to literally explode and crumble," said Transports Québec spokeswoman Sarah Bensadoun.

Transports Québec reports the overpass was last inspected and secured less than two months ago, on Nov. 27. Bensadoun said the weather fluctuations are the most likely explanation for the rapid degradation of the concrete around the overpass guardrail that was responsible for yesterday’s accident.

CAQ points to 2012 report

The opposition Coalition Avenir Québec's transportation critic, Éric Caire, questioned this explanation, saying a report from the last full inspection of the overpass in 2012 raised serious concerns about the concrete around the guardrails.

He questioned whether enough was done to address those concerns.

Damaged car Hymus

Falling debris from the Henri-Bourassa overpass damaged a car on Highway 40 on Monday. (Catherine Gauthier/Radio-Canada)

According to the president of concrete repair company Soconex, concrete won't normally crumble as it did because of weather, unless it's already in disrepair.

"You take a good piece of concrete, you put it from minus 20C to plus 20C, and you cover it with water, nothing would happen," said Normand Tétreault, who is also an engineer.

"If something happened ... related to freeze and thaw, the structure needs to be in poor condition or has to be cracked."

Compounding concerns is the number of similar incidents that have occurred in Montreal. 

In 2011, a 15-metre concrete beam fell from the Ville-Marie tunnel.

In 2006, five people died when a highway overpass collapsed in Laval and crushed two vehicles underneath.

Inspectors return tonight

Highway 40 was open to traffic this morning after officials closed it overnight to inspect the overpass and remove 4.8 square metres of superficial concrete.

Transports Québec is reminding the public that removed concrete was purely aesthetic, meant to hide the structure's inside.

"Be assured that if it was dangerous, the traffic would be not allowed," Bensadoun said.

Bensadoun said inspectors will be back at work on the overpass this evening. Highway 40 will remain open and only a service road will be closed during the inspection.

Transports Québec also said Tuesday that it will inspect 500 similar overpasses around the province, including hundreds in Montreal.